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From Stefan Guggisberg <stefan.guggisb...@gmail.com>
Subject Re: [MongoMK] Reading blobs incrementally
Date Wed, 17 Oct 2012 09:03:32 GMT
On Wed, Oct 17, 2012 at 10:42 AM, Michael Dürig <mduerig@apache.org> wrote:
> I wonder why the Microkernel API has an asymmetry here: for writing a binary
> you can pass a stream where as for reading you need to pass a byte array.

the write method implies a content-addressable storage for blobs,
i.e. identical binary content is identified by identical identifiers.
the identifier
needs to be computed from the entire blob content. that's why the
signature takes
a stream rather than supporting chunked writes.


> Michael
> On 26.9.12 8:38, Mete Atamel wrote:
>> Hi,
>> I realized that MicroKernelIT#testBlobs takes a while to complete on
>> MongoMK. This is partly due to how the test was written and partly due to
>> how the blob read offset is implemented in MongoMK. I'm looking for
>> feedback on where to fix this.
>> To give you an idea on testBlobs, it first writes a blob using MK. Then,
>> it verifies that the blob bytes were written correctly by reading the blob
>> from MK. However, blob read from MK is not done in one shot. Instead, it's
>> done via this input stream:
>> InputStream in2 = new BufferedInputStream(new MicroKernelInputStream(mk,
>> id));
>> MicroKernelInputStream reads from the MK and BufferedInputStream buffers
>> the reads in 8K chunks. Then, there's a while loop with in2.read() to read
>> the blob fully. This makes a call to MicroKernel#read method with the
>> right offset for every 8K chunk until the blob bytes are fully read.
>> This is not a problem for small blob sizes but for bigger blob sizes,
>> reading 8K chunks can be slow because in MongoMK, every read with offset
>> triggers the following:
>> -Find the blob from GridFS
>> -Retrieve its input stream
>> -Skip to the right offset
>> -Read 8K
>> -Close the input stream
>> I could fix this by changing the test to read the blob bytes in one shot
>> and then do the comparison. However, I was wondering if we should also
>> work on an optimization for successive reads from the blob with
>> incremental offsets? Maybe we could keep the input stream of recently read
>> blobs around for some time before closing them?
>> Best,
>> Mete

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